<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>

    <style>
        /*body总有一个默认的外边距margin:0，常见操作*/
        /*h1,ul,li,a,body{*/
        /*margin:0;*/
        /*padding:0;*/
        /*text-decoration:none;*/
        /*}*/
        /*border:粗细，样式，颜色*/
        #box{
            width:300px;
            border:1px solid red;
        }
        h2{
            font-size:16px;
            background-color:#3cbda6;
            line-height:30px;
            color:white;
        }
        form{
            background:#3cbda6;
        }
        div:nth-of-type(1) input{
            /*solid实线*/
            border:3px solid black;
        }
        div:nth-of-type(2) input{
            /*dashed虚线*/
            border:3px dashed #4d0b8c;
        }
        div:nth-of-type(2) input{
            border:2px dashed #008c27;
        }
    </style>

</head>
<body>

<div id="box">
    <h2>会员登录</h2>
    <form action="#">
        <div>
            <span>用户名:</span>
            <input type="text">
        </div>
        <div>
            <span>密码:</span>
            <input type="password">
        </div>
        <div>
            <span>邮箱:</span>
            <input type="email">
        </div>
    </form>
</div>

</body>
</html>